Failure To Create High Volume Email Account With Vague Error

If you try to create a High Volume Email account and the password you set for the account is not strong enough, neither the web interface or PowerShell cmdline will tell you that the password is no good, but will instead say “Internal Server Error” in the Exchange admin portal or the even more obscure “New-MailUser: Required field ExternalDirectoryObjectId was not returned from Graph API response during Member Creation.” when running PowerShell:

In the Exchange Admin Center, creating a High Volume Email account requests a password but gives no indication of lack of suitability for the string you enter (we used “banana” here as well):

Then click Next, followed by Create…

Changing the password string to something with capitals, lower, symbols and numbers and the High Volume Email account was created within a few seconds.

So, getting exactly this error – make your account password stronger and try again.